1. Field of the Invention
The present invention relates to a method of manufacturing products by forming and enclosing a body of powder in a casing and binding together and compacting the powder into a solid body by subjecting it to high temperature and a high all-sided pressure. A casing with an enclosed powder body is evacuated prior to and/or during the heating so that the powder body is degassed and, in this way, the substances which are harmful to the material are removed. The invention is of particular interest for the degassing operation in the manufacture of large billets of material of such a composition that manufacture by conventional casting methods gives unsatisfactory results, for example coarse structure or segregations. The method is particularly advantageous in the manufacture of billets of material of high-speed steel type or of superalloys for further machining to the desired shape by means of rolling, forging or machining.
2. The Prior Art
To construct an evacuation connection which results in a great surface for the escape of gas on the powder body but which simultaneously withstands the subsequent hot pressing, has proved to involve very great difficulties.
During the heating, the material in the capsule, the vacuum connection and particularly the joining welds and the material of adjoining parts change their properties and leaks occur when the capsule is deformed in the hot pressing. The difficulties have increased with increased capsule volume and with increased heating and heat retaining time prior to the hot-pressing. An increase in the capsule volume automatically involves an increase in the heating time and thus an increased risk of changes in the material which may give rise to leaks in the capsule when it is deformed during hot pressing. In one case, a funnel-shaped vacuum connection with an internal conical support body has been used to reduce the stresses. By means of that arrangement, the stresses in and at the joing between the capsule wall and the vacuum connection are reduced, and simultaneously a large powder body-surface liberating gases is obtained around the vacuum connection.